Pumpjack units are well known and have been provided with numerous different control apparatus for shutting in the pumpjack whenever a pump-off or fluid pounding condition is encountered by the downhole pump. Some of these prior art devices operate by weighing the bridle, as shown in Mills U.S. Pat. No. 4,363,605 for example; and other control devices are connected to sense slight movement or vibration of various structural components of the pumpjack unit as shown in Mills U.S. Pat. No. 4,631,954. All of these prior art control devices shut-in the well whenever fluid pounding is encountered. There are still other control devices that measure the operating variables of the electric motor that drives the pumpjack, as shown in Gibbs U.S. Pat. No. 3,951,209, and create an operating signal for shut-in. There are a multitude of flow control and flow measuring devices known to those skilled in the art for sensing the flow through a flow line, as evidenced by the following U.S. Pat. Nos. 2,293,574; 3,299,817; and 4,499,347.
The present invention constitutes an improvement over the prior art by the provision of a flow control device placed in a flow line and arranged to sense each flow produced by each reciprocation of the downhole pump. This cyclic flow is used to reciprocate a flow responsive member in proportion to the magnitude of the cyclic flow. When the member is displaced less than a predetermined amount a sensor associated therewith causes the well to be shut-in.